A poly(vinyl chloride) resin or a poly(vinyl chloride) resin filled with filler is sometimes used as a base material resin of a composite construction material in which a synthetic-resin surface layer material and the base material are layered. The surface layer material may be a resin of the same type as the poly(vinyl chloride) resin or a resin that is of a different type from the poly(vinyl chloride) resin but that adheres strongly to the poly(vinyl chloride) resin, for example, an ABS resin or an acrylic resin.
A styrene thermoplastic resin, such as an ABS resin or a PS resin, that has extrusion conditions relatively close to those of the poly(vinyl chloride) resin may be used in place of the poly(vinyl chloride) resin. The PS resin has excellent processibility, foam moldability, and appearance, and is inexpensive.
However, the PS resin has poor weatherability and low chemical resistance and is therefore unsuitable for a surface layer material (designed surface).
The ABS resin has excellent weatherability and high chemical resistance, as well as excellent processibility and appearance, but is more expensive than the PS resin.
Patent Document 1 describes a composite material that includes, as a base material resin (non-designed surface side), an inexpensive PS resin material having excellent foam moldability and a high-functionality ABS resin as a surface layer material (designed surface side). However, common coextruded ABS/PS composite products have the following disadvantages i) to v):
i) a product may get chipped (hereinafter referred to as “chipping”) in a cutting process during manufacture;
ii) a base material layer and a surface layer are likely to have insufficient adhesion therebetween, causing delamination in manufacturing processes;
iii) i) and ii) cause defective products, thus reducing the manufacturing yield;
iv) the durability of a product may be impaired by delamination between a base material layer and a surface layer during the use of the product; and
v) a surface layer of a molded product is susceptible to scratching during transfer.
Patent Document 2 describes incorporation of a waste resin or the like into a base material resin. The base material resin containing the waste resin tends to worsen the problems described above.    [Patent Document 1] Japanese Unexamined Patent Application Publication No. 63-115739    [Patent Document 2] Japanese Unexamined Patent Application Publication No. 2000-303743